SQL-DATABASE ERROR

Database error in WoltLab Burning Board (2.1.5): Invalid SQL: SELECT * FROM bb2_sponsoren WHERE showsponsor_b=1 AND sponsorpartner=0 ORDER BY RAND() desc LIMIT 1
mysql error: Disk full (/tmp/#sql_2be_0.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
mysql error number: 1021
mysql version: 10.1.48-MariaDB-0ubuntu0.18.04.1
php version: 5.3.29
Date: 08.06.2023 @ 08:19
Script: /register.php?sid=1ea4fcfd34ada9bfb89dd897771a7014
Referer: